Thermoregulation at mammals that live in water

About mammals > Adaptations for aquatic life

Most aquatic animals are ectotherms, or poikilotherms, orwhat is often referred to as “cold-blooded.” As the temperatureof the surrounding water rises and falls, so does theirbody temperature and, consequently, their metabolic rate.Many become quite sluggish in unusually cold water. This“slowing down” caused by cold water is a disadvantage for activeswimmers. Some large fish, such as certain tunas andsharks, can maintain body temperatures that are considerablywarmer than the surrounding water. They do this by retainingthe heat produced in their large and active muscles. Thisallows them to remain active even in cold water.

Aquatic mammals are able to keep their body temperaturesmore or less constant regardless of water temperature. Marinemammals deposit most of their body fat into a thick layerof blubber that lies just underneath the skin.

This blubberlayer not only insulates them but also streamlines the bodyand functions as an energy reserve. The fusiform body shapeand reduced limb size of many marine mammals and organismsdecreases the amount of surface area exposed to the externalenvironment. This helps conserve body heat. Aninteresting example of this body form adaptation can be seenin dolphins: those adapted to cooler, deeper water generallyhave larger bodies and smaller flippers than coastal dolphins,further reducing the surface area of their skin.

Arteries in the flippers, flukes, and dorsal fins of marinemammals are surrounded by veins. Thus, some heat from theblood traveling through the arteries is transferred to the venousblood rather than the outside environment. This countercurrentheat exchange also helps to conserve body heat.